1. Field of the Invention
The present invention relates generally to a sensor system for monitoring the structural integrity of an underground waste containment barrier, and leakage therefrom of waste products or byproducts, and for improved characterization of zones of interest.
2. Background Art
It is often necessary to form a containment barrier around a hazardous waste site to stop or prevent the migration of contaminants into the nearby soil and water tables. The containment barrier must prevent the migration of contaminants both horizontally and vertically away from the waste site. Therefore, a properly constructed containment barrier may be compared to a huge bathtub, with the hazardous waste contained within four side walls and a generally horizontal floor.
A typical, currently-used method of containment is to physically remove the hazardous waste and haul it to a permitted storage facility. However, such method is costly, impractical, and dangerous. Digging up sites with buried drums, radioactive dusts, or other airborne wastes may actually release the contaminants, spreading them into the atmosphere and through the soil.
In response to this problem, a number of suggestions have been made for placing containment barriers around hazardous waste sites, without removing the waste. One approach for doing this is disclosed in International Publication Nos. WO 94/19547 and WO 93/00483 by Halliburton Nus Environmental Corp. The Halliburton system uses a row of high pressure jets to shoot a slurry into soil surrounding a hazardous waste site, somewhat liquefying the surrounding soil. The slurry cuts a path through the soil as it intermixes with the liquified soil. Gravity and/or mechanical means pull the row of high pressure jets through the mix of liquified soil and slurry, after which the liquified soil and slurry harden into a protective barrier.
The above-described system has a number of shortcomings, including the possibility of further spreading contaminants by the use of hydraulic jets, the difficulty of maintaining balance between the amount of slurry needed for cutting and the amount of slurry needed for hardening the soil, the difficulty of providing a barrier of consistent strength since it would depend in part upon the soil composition encountered and the amount of slurry deposited, and, finally, the lack of testing of excavated soil to know whether soil surrounding the waste site has become contaminated.
Another suggested approach for installing a containment barrier around a hazardous waste site is disclosed in patent application Ser. No. 08/925,101, filed Sep. 8, 1997, now U.S. Pat. No. 6,016,714 issued Jan. 25, 2000. In this approach, a multi-layer containment barrier is put in place under a hazardous waste site without disturbing any buried waste, in a simple and efficient fashion. The disclosure in the above-noted co-pending patent application is incorporated herein by reference.
In any approach to holding hazardous waste, it would be desirable to monitor the site in terms of both the structural integrity of any containment barrier put in place about the waste material, and leakage of contaminants away from the site. Additionally, it would be desirable to monitor material being excavated from around a waste site in preparation for emplacement of a containment barrier for the site, to determine the extent of contamination of surrounding soils and thus the possible need to extend the containment barrier to a location completely surrounding all contaminated materials and soils. Finally, it would be desirable to efficiently and inexpensively install a long-term monitoring system soon after or simultaneously with the installation of the containment barrier.